A communications network may comprise a number of nodes which are connected by communication paths or links. There may be many possible channels which can be used to communicate between two nodes over a single communication path. These channels may be defined by parameters, which may include, but are not limited to, frequency (i.e carrier frequency), coding scheme, time slot and beam selection.
Before data can be transmitted across a communication path, it is necessary to decide which channel should be used. Each of the channels is unlikely to provide an equal quality link and this is particularly true in the case of wireless links which will be affected by interference from other radio sources in the vicinity and also from communications across other paths in the network.
Several techniques have been proposed to select a channel in order to be able to transmit data. In some situations the quality of each channel is measured prior to making the selection and the best quality channel is selected. This requires a lot of measurement overhead in order to determine the best channel and may require additional signalling.
In GSM and Bluetooth a technique of frequency hopping is used. Both the nodes which are communicating switch between frequencies according to the same predetermined pattern. This uses all possible channels for a short period of time each and ensures that nodes do not dwell on a poor quality channel.
Alternatively, the network can include an overall control entity which manages allocation of channels for communication paths. However, in some circumstances the use of an overall control entity is problematic. Reasons for this include inflexibility to changes in network structure and environmental conditions etc and also large computational and signalling overheads. Additionally, a system using an overall control entity does not scale well.